It is known to secure the shank of such a tool by means of a press fit in a central receiving opening of an annular, intrinsically closed tool holder part usually embodied in the form of a sleeve part. This sleeve part constitutes the tool end of a tool holder of an otherwise conventional design.
The above-mentioned part or sleeve part of the tool holder can be expanded with heat in the radial direction until the cold shank of the tool can be inserted into or removed from the sleeve part. As soon as the sleeve part has cooled again, a press-fit connection is established between it and the shank of the tool, thus reliably securing the tool in the tool holder (shrink-fit technology, for example see EP 1 353 768 B1).
Alternatively, hydraulic clamping is also possible. For this purpose, a hydraulic clamping mechanism is situated inside the above-mentioned part of the tool holder and when acted on with hydraulic pressure, reduces its inner diameter encompassing the tool shank, thus clamping the tool shank in a frictional fashion.
As a third alternative, it is possible for the pressure required for secure frictional clamping of the tool shank to be exerted by purely mechanical means, for example by means of collet chucks according to DIN ISO 15488 or EP 1 291 103 or roller jaw chucks according to DE 35 172 46.
Clamping chucks of the above-described type have proven valuable in practice.
However, there is still the problem already reported by German patent DE 199 26 209 that with a hard clamping of the shank, during operation, stresses in the form of a circumferential bending stress can occur (the above-mentioned patent refers to these stresses as a “walking effect”), which can sometimes result in a fatigue fracture of the tool shank.
In order to solve this problem the above-mentioned patent proposes providing damping cavities in the tool receptacle sleeve part that constitutes the actual clamping chuck. These damping cavities, embodied in the form of hollows, are sunk into the sleeve part from its end surface. However, it is only possible to achieve this with relatively complex production processes such as erosion.
As the above-cited patent correctly states, the damping cavities make the clamping of the tool shank “softer.” As a result, the “cardan effects” that occur due to the otherwise hard clamping of the shank (as in DE 199 26 209) and that can lead to breakage of the tool shank are prevented or largely prevented—or to express it in other words: by permitting the tool shank to diagonally tilt by a small amount in the tool receptacle, which is no longer quite so rigid, the circumferential bending stress that this tool shank experiences, particularly during circumferential milling, decreases in comparison to the bending stress that occurs with a rigid clamping of the tool shank.
There are a few disadvantages, however, to the sinking of the damping cavities into the sleeve part as proposed by the above-mentioned patent DE 199 26 209. The production of the damping cavities in the sleeve part incurs some manufacturing costs. In addition, it is not possible to produce a limitless variety of geometries for the damping cavities in the sleeve part; on the contrary, there is only a limited range from which to select. Due to the minimal number of embodiment options, it is difficult to precisely achieve the desired damping characteristics using the damping cavities proposed by DE 199 26 209.
Furthermore, the damping characteristics of a tool holder can no longer be changed once the damping cavities have been sunk into its sleeve part.
By contrast, one object of the invention is to disclose a tool holder whose damping characteristics can be more freely selected while being simpler to produce.